1. Field of the Invention
The field of invention is associated with providing artificial lift to a well producing hydrocarbon fluid. More specifically, the field relates to providing artificial lift using an electrochemical gas lift apparatus and method.
2. Description of the Related Art
At the beginning of the hydrocarbon fluid production cycle, the fluid pressure trapped in the hydrocarbon-bearing formation is operable to drive hydrocarbon fluid to the surface through a pre-formed well bore without additional production assistance. The pressure difference between the fluid head pressure present in the well bore and the pressure of the hydrocarbon fluid in the hydrocarbon-bearing is sufficient to have consistent and predictable production of hydrocarbon fluids from the well bore for a time into the future—potentially years.
Eventually, the pressure in the hydrocarbon-bearing formation diminishes and hydrocarbon fluid production falls. At a certain point, the pressure present in the hydrocarbon-bearing formation is no longer sufficient to produce hydrocarbon fluid at a desirable hydrocarbon fluid flow rate.
Artificial lift techniques can assist in producing hydrocarbon fluids at a desired flow rate. Electric submersible pumps (ESPs) push hydrocarbon liquids to the surface by boosting their pressure downhole. Surface pumps reduce the liquid head pressure and pull hydrocarbon liquids to the surface. Hydraulic injection systems can introduce fluid into the well to drive hydrocarbon liquids to the surface by powering subsurface pumps. Hydraulic injection systems can introduce chemicals into the well bore that lower the viscosity of the hydrocarbons downhole, making them easier to pump uphole. Gas lift systems inject compressed gas to the bottom of the well to help reduce hydrocarbon fluid head pressure by lowering the density of the fluid uphole.
Current gas lift systems suffer from major flaws. First, they require a constant and large source of compressible gas to inject into the well to provide an effective amount of fluid lift downhole. Due to the difference in pressure between the surface and the bottom of the well, a large amount of surface gas is required to achieve desirable amounts of gas lift of the bottom due to compression. A fixed gas injection system with a pipeline to a reliable gas production source or an on-site system with storage facilities in a remote location is very expensive to construct and can be operationally unreliable. Second, the compressed gas, pressurized to overcome the fluid head pressure at the point of discharge downhole, is cold—possibly well below the freezing temperature of water. Raw hydrocarbon fluids contain formation water and hydrocarbon gases that can freeze and form complex hydrocarbon hydrates when in contact with cold surfaces. Clathrates tend to build up against cold surfaces and block fluid flow pathways. Production downtime and intervention to break apart a frozen well bore is expensive. Finally, the selection of injection gases is problematic. Using air introduces a lot of oxygen and some carbon dioxide, which surface gas processing systems must remove from the produced associated gas. These compounds can also form reactive species in the well bore environment that interact with the hydrocarbon and non-hydrocarbon bearing formation in undesirable ways. Pre-refined and on-site separated atmospheric gas processing is expensive, requiring specialized transportation, storage and pre-heating facilities before use.
Electrolysis is the passage of an electrical current through an electrolyte and migration of disassociated charged ions to opposite-charged electrodes. Electrolysis of an electrically-conductive aqueous solution can produce both hydrogen and halogen gases (that is, chlorine, fluorine, bromine, and iodine) as reaction products from solutions containing dissolved metal halides, including salts and minerals, for example, NaCl, CaCl2, MgCl2, CaSO4, Na2SO4, MgBr2, NaBr and KCl. Electrolysis of an aqueous solution of metal halide containing sodium can produce a halogen gas and a hydrogen gas as shown in Equation 1:2NaX(aq.)+2H2O(l)→X2(g)+2NaOH(aq.)+H2(g)  (Eq. 1),where X is the halogen specie. The halogen gas forms at the anode (“anode product gas”) and hydrogen gas forms at the cathode (“cathode product gas”). In addition, a small amount of hydroxide ions can disassociate at the anode and provide a small amount of by-product oxygen as shown in Equation 2:4OH—(aq.)→2H2O(l)+O2(g)  (Eq. 2).If hydrogen gas and halogen gas recombine at any point, the two gases can form a hydrogen-halogen gas as shown in Equation 3, which in the aqueous solution environment can then form an acidic solution as shown in Equation 4:H2(g)+X2(g)→2HX(g)  (Eq. 3), andHX(g)+H2O(l)→HX(aq.)+H2O(l)  (Eq. 4).